1. Field of the Invention
The present invention relates to a process for producing ceramic sintered products having high strength and, more particularly, it relates to alumina sintered products for use as cutting tools or other abrasion resistant parts.
2. Description of the Prior Art
Hitherto for, as sintering additives for alumina ceramics having high strength used as ceramic tools and other abrasion resistant parts, MgO, NiO, CaO, SiO.sub.2, ZrO.sub.2 and the like have been known. Of these, MgO has been the most generally used. Recently, however, the requirements of ceramic tools have become more demanding and tools having greater strength and higher abrasion resitance are required. Only alumina-carbide tools such as an alumina-titanium carbide have been used as ceramic tools for high speed cutting or heavy cutting, etc., because conventional high purity alumina ceramic tools possessing an alumina content of about 95 wt% or more have poor antibreaking property and abrasion resistance. However, alumina-titanium carbide tools, for example, suffer from abnormal abrasion during microfinish cutting at high-speeds, cutting of hard materials, cutting of ductile cast iron, etc. due to the influence of the TiC component contained therein. Accordingly, it has been desired to develop tools which do not contain a TiC component or which are not adversely affected by the TiC component.
The so-called conventional high purity alumina ceramics have an average crystal size of about 3.mu. or more and a porosity of about 0.1% by volume, when produced by a hot press process. If it is intended to limit the porosity to about 0.1% by volume or less when MgO is added, higher sintering temperatures are required and, consequently, the crystals naturally grow and the average crystal grain size exceeds about 10 microns. Thus, it is extremely difficult to achieve the porosity limitation. For example, alumina-TiC tools have a porosity of about 0.1% by volume or less and the average crystal size of about 1 to 2.mu..